Dino Villagrán

Synthesis, Structures, and Properties of 1,2,4,5-Benzenetetrathiolate Linked Group 10 Metal Complexes

Dimetallic compounds [(P-P)M(S(2)C(6)H(2)S(2))M(P-P)] (M = Ni, Pd; P-P = chelating bis(phosphine), 3a-3f) are prepared from O=CS(2)C(6)H(2)S(2)C=O or (n)Bu(2)SnS(2)C(6)H(2)S(2)Sn(n)Bu(2), which are protected forms of 1,2,4,5-benzenetetrathiolate. Selective monodeprotections of O=CS(2)C(6)H(2)S(2)C=O or (n)Bu(2)SnS(2)C(6)H(2)S(2)Sn(n)Bu(2) lead to [(P-P)Ni(S(2)C(6)H(2)S(2)C=O)] or [(P-P)Ni(S(2)C(6)H(2)S(2)Sn(n)Bu(2))]; the former is used to prepare trimetallic compounds [(dcpe)Ni(S(2)C(6)H(2)S(2))M(S(2)C(6)H(2)S(2))Ni(dcpe)] (M = Ni (6a) or Pt (6b); dcpe = 1,2-bis(dicyclohexylphosphino)ethane). Compounds 3a-3f are redox active and display two oxidation processes, of which the first is generally reversible. Dinickel compound [(dcpe)Ni(S(2)C(6)H(2)S(2))Ni(dcpe)] (3d) reveals two reversible oxidation waves with DeltaE(1/2) = 0.66 V, corresponding to K(c) of 1.6 x 10(11) for the mixed valence species. Electrochemical behavior is unstable to repeated scanning in the presence of [Bu(4)N][PF(6)] electrolyte but indefinitely stable with Na[BArF(24)] (BArF(24) = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate), suggesting that the radical cation generated by oxidation is vulnerable to reaction with PF(6)(-). Chemical oxidation of 3d with [Cp(2)Fe][BArF(24)] leads to formation of [3d][BArF(24)]. Structural identification of [3d][BArF(24)] reveals appreciable shortening and lengthening of C-S and C-C bond distances, respectively, within the tetrathioarene fragment compared to charge-neutral 3d, indicating this to be the redox active moiety. Attempted oxidation of [(dppb)Ni(S(2)C(6)H(2)S(2))Ni(dppb)] (3c) (dppb = 1,2-bis(diphenylphosphino)benzene) with AgBArF(24) produces [[(dppb)Ni(S(2)C(6)H(2)S(2))Ni(dppb)](2)(mu-Ag(2))][BArF(24)](2), [4c][BArF(24)](2), in which no redox chemistry has occurred. Crystal structures of bis(disulfide)-linked compounds [(P-P)Ni(S(2)C(6)H(2)(mu-S(2))(2)C(6)H(2)S(2))Ni(P-P)] are reported. Near IR spectroscopy upon cationic [3d](+) and neutral 6a reveals multiple intense absorptions in the 950-1400 nm region. Time-dependent density functional theory (DFT) calculations on a 6a model compound indicate that these absorptions are transitions between ligand-based pi-type orbitals that have significant contributions from the sulfur p orbitals.

Pseudotetrahedral d0, d1, and d2 metal-Oxo cores within a Tris(alkoxide) platform

Low-coordinate first-row metal complexes of d(0) [vanadium(V)], d(1) [chromium(V)], and d(2) [chromium(IV)] assume the unusual ligand field of a pseudotetrahedron when supported by a tripodal tBu(2)(Me)CO(-) alkoxide framework. Structural, spectroscopic, and reactivity studies, supported by density functional theory calculations, indicate that the d electrons in the chromium(V) and -(IV) oxo complexes reside in metal-oxygen antibonding orbitals, engendering disparate reactivity of the metal-oxo, depending on the number of d electrons present.

Iron in a trigonal tris(alkoxide) ligand environment

Mononuclear Fe(II) and Fe(III) complexes residing in a trigonal tris(ditox) (ditox = (t)Bu2(Me)CO(-)) ligand environment have been synthesized and characterized. The Fe(III) ditox complex does not react with oxidants such as PhIO, whereas NMe3O substitutes a coordinated tetrahydrofuran (THF) in the apical position without undergoing oxo transfer. In contrast, the Fe(II) ditox complex reacts rapidly with PhIO or Me3NO in THF or cyclohexadiene to furnish a highly reactive intermediate, which cleaves C-H bonds to afford the Fe(III)-hydroxide complex. When generated in 1,2-difluorobenze, this intermediate can be intercepted to oxidize phosphines to phosphine oxide. The fast rates at which these reactions occur is attributed to a particularly weak ligand field imparted by the tris(alkoxide) ancillary ligand environment.

Dinitrogen binding at vanadium in a tris(alkoxide) ligand environment

We report the first tris(alkoxide)V(III) complex to bind dinitrogen. Removal of THF from V(OR)(3)THF furnishes the highly reactive V(OR)(3) fragment, which binds dinitrogen to form [V(OR)(3)](2)(μ-N(2)) in the solid state. Dinitrogen is readily released upon dissolution of the complex. Structural and DFT studies are consistent with significant activation of N(2) when bound by the vanadium tris(alkoxide) platform.

Manipulating Magnetism: Ru25+ Paddlewheels Devoid of Axial Interactions

Variable-temperature magnetic and structural data of two pairs of diruthenium isomers, one pair having an axial ligand and the formula Ru2(DArF)4Cl (where DArF is the anion of a diarylformamidine isomer and Ar = p-anisyl or m-anisyl) and the other one being essentially identical but devoid of axial ligands and having the formula [Ru2(DArF)4]BF4, show that the axial ligand has a significant effect on the electronic structure of the diruthenium unit. Variable temperature crystallographic and magnetic data as well as density functional theory calculations unequivocally demonstrate the occurrence of π interactions between the p orbitals of the chlorine ligand and the π* orbitals in the Ru2(5+) units. The magnetic and structural data are consistent with the existence of combined ligand σ/metal σ and ligand pπ/metal-dπ interactions. Electron paramagnetic resonance data show unambiguously that the unpaired electrons are in metal-based molecular orbitals.

In,V-codoped TiO2 nanocomposite prepared via a photochemical reduction technique as a novel high efficiency visible-light-driven nanophotocatalyst

In the current study, a series of novel, high efficiency photocatalysts of In,V-codoped TiO2 were developed. The TiO2 nanoparticles were synthesized by sol–gel and hydrothermal methods and different molar percentages (0.1–1%) of vanadium (V) and Indium (In) nanoclusters were deposited over the TiO2 nanoparticles via photochemical reduction. XRD, SEM, EDX, TEM, XPS and UV-vis DRS analyses were carried out to characterize the prepared In,V-codoped TiO2 nanocatalysts, and methyl orange (MO) was used as the probe environmental pollutant to test the photocatalytic performance of the prepared catalysts under UV and visible light irradiation. Our study demonstrated that In and V nanoclusters were successfully deposited over TiO2 particles via a photochemical deposition technique and the metal doping slightly suppressed TiO2 crystal growth. The optical analysis showed a red shift in the light absorption spectrum and decrease in the band gap of In,V-codoped TiO2 catalysts compared to that of parent TiO2. XPS study revealed that the doped elements In and V are in oxidation state of 3 (InIII), 4 (VIV) and 5 (VV). The photo-oxidative decomposition of MO showed that doping of In and V can considerably improve the photocatalytic activity of TiO2. Thus, for the first time, we demonstrated that TiO2 codoped with binary metals of In and V can serve as a high efficiency visible-light-active photocatalyst.

A Convergent Approach to the Synthesis of Multimetallic Dithiolene Complexes

Controlled base hydrolysis of one or both of the protected 1,2-dithiolene chelates of 1,3,5,7-tetrathia- s-indacene-2,6-dione (OCS 2C 6H 2S 2CO) enables the stepwise synthesis of di- and trimetallic complexes with 1,2,4,5-benzenetetrathiolate as the connector. Treatment of OCS 2C 6H 2S 2CO with MeO (-), followed by [NiBr 2(dcpe)] [dcpe = 1,2-bis(dicyclohexylphosphino)ethane], yields [(dcpe)Ni(S 2C 6H 2S 2CO)] ( 4). The reaction of 4 with EtO (-), followed by [MX 2(dcpe)] (X = halide), yields [(dcpe)Ni(S 2C 6H 2S 2)M(dcpe)] [M = Ni ( 5a), Pd ( 5b)]. Deprotection of the 1,3-dithiol-2-one group of 4, followed by introduction of (1)/ 2 equiv of MX 2 and then I 2, yields the neutral trimetallic compounds [(dcpe)Ni(S 2C 6H 2S 2)] 2M [M = Ni ( 6a), Pt ( 6b)]. Tetrahedralization at nickel is observed in 5a, which density functional theory calculations attribute to second-order Jahn-Teller effects, while 6a and 6b display an end-to-end folding of approximately 46 degrees . A color darkening is observed in moving from 4 to compounds 6 due to the increasing size of the conjugated metal-organic pi system. Intense, broad absorptions in the near-IR are observed for 6a and 6b.

Band gap and Schottky barrier engineered photocatalyst with promising solar light activity for water remediation

A novel nanophotocatalyst of Mo- and S-doped TiO2 (Mo,S-codoped TiO2) was synthesized via a modified sol–gel method in conjunction with photochemical reduction. The XRD results showed that all of the prepared nanocatalysts only contain the anatase phase. The SEM and TEM analyses revealed that the doping of Mo and S does not cause any change in the morphology of the TiO2 catalyst. Chemical composition analysis carried out using EDX confirmed the successful doping of TiO2 by Mo and S, and DRS illustrated band gap reduction in TiO2 after doping. The photocatalytic performance of the samples was tested using the degradation of methyl orange (MO) as a model organic pollutant. The results showed that the photocatalytic activity of the Mo(0.06%), S(0.05%)-codoped TiO2 catalyst was higher than that of other catalysts under UV and visible light irradiation. Indeed, due to the synergetic effect of doping S and Mo, the Mo,S-codoped TiO2 catalyst has a higher photoactivity than the pure TiO2 and TiO2 doped solely with either Mo or S. Finally, it is proposed that the newly developed Mo,S-codoped TiO2 photocatalyst could be a great candidate for environmental applications such as air and water purification.

Emerging opportunities for nanotechnology to enhance water security

No other resource is as necessary for life as water, and providing it universally in a safe, reliable and affordable manner is one of the greatest challenges of the twenty-first century. Here, we consider new opportunities and approaches for the application of nanotechnology to enhance the efficiency and affordability of water treatment and wastewater reuse. Potential development and implementation barriers are discussed along with research needs to overcome them and enhance water security.This Perspective provides an overview of the potential aspects of water treatment and cleaning in which nanotechnology could play an important role.